Laser fusible redundancy technology plays a key role for improving the yield of today's high density memory chips. However, disadvantages exist associated with such technology. For example, devices produced according to the technology are bulky and costly in terms of chip area. The fuse blowing process that may occur in devices according to this technology may not operate as desired. The fuse blowing process is time consuming and unreliable, and the fuses are not reprogrammable.
As memory circuits become more sophisticated, it is often necessary to incorporate a block of EEPROM into other memory arrays, such as DRAM or SRAM. One example of such a device is a "smart card". In a smart card, RAM serves as a scratch pad, ROM stores programs and runs the card's operating system, EEPROM includes user data, and a microcontroller allocates the memory and runs an encryption program. One example of a smart card is described in John Gallant, Smart Cards, EDN, Nov. 23, 1995, pp. 34-42, the entire disclosure of which is hereby incorporated by reference.
It is a great challenge to design a high density, small chip size, low cost smart card integrated circuit. Such devices have many inherent problems. For example, chip sizes larger than 25 mm.sup.2 are prone to experiencing fractures when a card is flexed. Nevertheless, mixed memory process integration will become necessary in, for example, system-on-chip (SOC) applications, where CPU, SRAM type cache, programmable memory arrays, and/or random accessible memory arrays, and/or other devices are integrated in or on the same chip.